The field of the invention is solid state power converters for use in regenerative motor controllers.
A motor controller converts the fixed-frequency AC power line voltage to a voltage and current suitable for driving the selected electric motor. An AC motor controller, for example, is commonly comprised of two sections: a power converter; and a motor inverter. The power converter connects to the line voltage and produces a controlled voltage on a DC bus which connects to the input of the motor inverter. The motor inverter generates an AC current for the motor which produces the desired motor speed and torque.
When motors are decelerated, they regenerate power. A motor inverter passes this regenerated power back to the DC bus where it is either dissipated by a resistor which is connected across the bus by a chopper circuit, or it is regenerated back to the power lines by the power converter. A number of regenerative power converters are known in the art, and as disclosed in U.S. Pat. No. 4,353,023 these typically employ silicon controlled rectifiers (SCR's) as the solid state control elements. These prior regenerative power converters feed a significant fraction of the regenerated power back into the power lines as reactive, or harmonic, power rather than real power. This results in a low power factor, which in turn, lowers the efficiency of the power converter and the motor drive. In addition, SCR converters are troublesome because SCR's are difficult to turn off once they are turned on and complex mode switching circuitry is required to accomodate changes in the direction of power flow.